Medication dispensing apparatus with triple screw threads for mechanical advantage

ABSTRACT

A medication dispensing apparatus that provides a mechanical advantage. During dose preparing, a nut rotating element ( 410 ) and a screw element ( 368 ) are in a first axial arrangement such that a screwing motion of the nut rotating element and screw element relative to the apparatus housing that moves the elements a first axial distance from a home position screws a nut ( 364 ) along a drive member threaded shaft ( 362 ) a second axial distance different than the first axial distance. During dose dispensing, the nut rotating element and the screw element are in a second axial arrangement, whereby a screwing motion of the screw element relative to the housing back toward the home position advances a plunger ( 366 ) in the distal direction to axially advance the nut and thereby the drive member and a fluid container piston to dispense medicine.

BACKGROUND OF THE INVENTION

The present invention pertains to medication dispensing devices, and, inparticular, to a portable medication dispensing device such as aninjector pen.

Patients suffering from a number of different diseases frequently mustinject themselves with medication. To allow a person to conveniently andaccurately self-administer medicine, a variety of devices broadly knownas injector pens or injection pens have been developed. Generally, thesepens are equipped with a cartridge including a piston and containing amulti-dose quantity of liquid medication. A drive member, extending fromwithin a base of the injector pen and operably connected with typicallymore rearward mechanisms of the pen that control drive member motion, ismovable forward to advance the piston in the cartridge in such a mannerto dispense the contained medication from an outlet at the oppositecartridge end, typically through a needle that penetrates a stopper atthat opposite end. In disposable or prefilled pens, after a pen has beenutilized to exhaust the supply of medication within the cartridge, auser, who then begins using a new replacement pen, discards the entirepen. In reusable pens, after a pen has been utilized to exhaust thesupply of medication within the cartridge, the pen is disassembled toallow replacement of the spent cartridge with a fresh cartridge, andthen the pen is reassembled for its subsequent use.

A number of known injection pens have utilized a mechanical advantage tofacilitate operation. An injection pen disclosed in InternationalPublication Number WO 96/26754 obtains a mechanical advantage with agear set including first and second coaxial pinions that engagedifferent racks within the pen, and which gear set travels with the penthrust rod. Another injection pen with a mechanical advantage isdisclosed in International Publication Number WO 01/95959, which penuses one or more gear wheels carried by a connector element threadedlyengaged with a piston rod. While these pens may be useful, their abilityto provide high mechanical advantage may be limited by, for example, howsmall the gears can be made. In addition, these pens have relativelycomplicated designs, as well as potentially costly components, such asseparate springs, which may undesirably impact the ability toeffectively commercialize the pen in a disposable format.

Some other known injection pens that provide mechanical advantage havecomplicated designs that may make them relatively expensive to produce.Still another injection pen, such as disclosed in U.S. Pat. No.5,938,642, is highly effective as a pre-filled device, but does notprovide a mechanical advantage during injecting.

Thus, it would be desirable to provide an apparatus that can overcomeone or more of these and other shortcomings of the prior art.

BRIEF SUMMARY OF THE INVENTION

In one form thereof, the present invention provides a medicationdispensing apparatus including a housing, a drive member rotatably fixedduring dose preparing and injecting and axially movable in a distaldirection relative to the housing, which drive member includes athreaded shaft, a fluid container defining a medicine-filled reservoirwith a movable piston at one end and an outlet at the other end, whichpiston is engagable by the drive member to be advanced toward the outletwhen the drive member is moved distally, a nut screwable along the drivemember threaded shaft, a screw element threadedly engaged with thehousing to be screwable relative to the housing, a nut rotating elementconnected with the nut to be axially movable and rotatably fixedrelative thereto, which nut rotating element is rotatably fixed with thescrew element when the nut rotating element and the screw element are ina first axial arrangement, which nut rotating element is rotatablerelative to the screw element when the nut rotating element and thescrew element are in a second axial arrangement, and a nut advancingplunger threadedly engaged with the screw element, which plunger isaxially movable and rotatably fixed relative to the housing. During dosepreparing, the nut rotating element and the screw element are in thefirst axial arrangement, whereby a screwing motion of the nut rotatingelement and screw element relative to the housing screws the nutrotating element and the screw element a first axial distance from ahome position, which screwing motion of the nut rotating element screwsthe nut along the drive member threaded shaft a second axial distancedifferent than the first axial distance. During dose dispensing, the nutrotating element and the screw element are in the second axialarrangement, whereby a screwing motion of the screw element relative tothe housing back toward the home position advances the plunger in thedistal direction to axially advance the nut and thereby the drive memberand the fluid container piston to dispense medicine from the outlet.

One advantage of the present invention is that a medication dispensingapparatus can be provided with a mechanical advantage that makes easierthe plunging needed to dispense medication, which mechanical advantagecan be very high and conveniently selected by the manufacturer duringapparatus design.

Another advantage of the present invention is that a medicationdispensing apparatus can be provided with an externally accessibleplunging member that when plunged travels a greater distance than thecartridge piston engaging drive member it advances, whereby even smallerdoses achieved with shorter drive member movements can involvemeaningful plunging member motion.

Still another advantage of the present invention is that a medicationdispensing apparatus can be provided which is mechanically efficient,and the high level of this efficiency may allow suitable operatingcharacteristics of the apparatus to be achieved even with less expensivecomponent parts.

Still another advantage of the present invention is that a medicationdispensing apparatus can be provided which can be made from a number ofparts and at a cost which makes it justifiably disposable after itsmedication contents are exhausted.

Yet another advantage of the present invention is that a medicationdispensing apparatus can be provided with a compact design thatcontributes to a short axial length and a small diameter of theapparatus.

Yet another advantage of the present invention is that a medicationdispensing apparatus can be provided which achieves a rotate to set avariable, desired dose, push to inject dose functionality with a limitedamount of parts and complexity.

Yet another advantage of the present invention is that a medicationdispensing apparatus can be provided which may be relatively low costdue to the use of compliant plastic to achieve functionality rather thanmetal springs.

Yet another advantage of the present invention is that a medicationdispensing apparatus can be provided with a high mechanical advantagethat does not require any small gears having a performance that may beuncertain due to, for example, the possibility of the teeth of the gearsfailing during operation if injection molded from an inexpensiveplastic.

Another advantage of the present invention is that a medicationdispensing apparatus can be provided with an integral insufficientremaining dose indicator that does not impact the force required toinject or set a dose.

Still another advantage of the present invention is that a medicationdispensing apparatus can be provided that does not require a dedicatedanti-back drive feature, or an injection clicker, and as a result theapparatus can be less complicated in design.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other advantages and objects of this invention,and the manner of attaining them, will become more apparent, and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taking in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a front perspective view of a first embodiment of a medicationdispensing apparatus with mechanical advantage of the present invention,which apparatus is capped as well as arranged in a ready or zero dosestate;

FIG. 2 is a front view in longitudinal cross-section of the medicationdispensing apparatus of FIG. 1;

FIG. 3 is a front perspective view in longitudinal cross-section of themedication dispensing apparatus of FIG. 1, but with the apparatus capremoved, with a needle assembly attached, and after the apparatus hasbeen manipulated from its ready state to a ready-to-inject state;

FIG. 4 is an enlarged view of select portions of the apparatus of FIG. 3during the initial actuator plunging associated with injecting;

FIG. 5 is an exploded, perspective view of portions of the apparatus ofFIG. 2;

FIG. 6 is a longitudinal cross-sectional view of portions of FIG. 5;

FIGS. 7-18 are longitudinal cross-sectional views of an assemblysequence of the medication dispensing apparatus of FIG. 1;

FIG. 19 is a partial front view in longitudinal cross-section of anothermedication dispensing apparatus of the present invention;

FIG. 20 is a partial front view in longitudinal cross-section of stillanother medication dispensing apparatus of the present invention;

FIG. 21 is a partial front view in longitudinal cross-sectionconceptually similar to the view of FIG. 20, but after the dismountingof the cartridge retainer from the housing;

FIG. 22 is a front perspective view of another embodiment of amedication dispensing apparatus with mechanical advantage of the presentinvention, which apparatus is capped as well as arranged in a ready orzero dose state;

FIG. 23 is a front view in longitudinal cross-section of the medicationdispensing apparatus of FIG. 22, wherein a capped needle assembly isshown provided;

FIG. 24 is a front perspective view in longitudinal cross-section of themedication dispensing apparatus of FIG. 23, but with the apparatus capremoved, and after the apparatus has been manipulated from its readystate to a ready-to-inject state in which a maximum dose is to bedispensed;

FIG. 25 is an exploded, perspective view of the apparatus of FIG. 23;and

FIG. 26 is a longitudinal cross-sectional view of the apparatus of FIG.25.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of the present invention, the drawings are not necessarilyto scale, and certain features may be exaggerated or omitted in some ofthe drawings in order to better illustrate and explain the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-3, there is shown a first embodiment of amedication dispensing apparatus of the present invention. Anydirectional references in this detailed description with respect to FIG.1 or any of the other Figures, such as right or left, upper or lower, orclockwise or counterclockwise, are intended for convenience ofdescription, and by itself does not limit the present invention or anyof its components to any particular positional or spatial orientation.

The apparatus, generally designated 20, is shown as an injector pen,which pen has an elongated, substantially writing instrument-like form,although other forms are within the scope of the invention. Medicationinjector pen 20 is a disposable or prefilled pen, in that after thequantity of medicine contained therein is exhausted by multipleoperations of the pen, the entire pen is discarded rather than beingreset and reloaded with a replacement container of medicine. Pen 20 isoperable by a user to select and then inject any one of a number ofdifferent size doses, such as may be appropriate with some therapeuticsloaded therein by the manufacturer, for example insulin. Pen 20 can alsobe adapted to deliver a dose in a specific amount appropriate for someother types of therapeutics loaded therein by the manufacturer.

Injector pen 20 generally includes a distal portion 22 and a proximalportion 24. Distal portion 22 contains the medicinal fluid to be outletat its distal end upon pen operation, and this portion is shown receivedwithin pen cap 21 in FIGS. 1 and 2. The outlet end of distal portion 22is equipped in FIG. 3 with an injection needle. Proximal portion 24contains the injecting mechanism used to force the contained medicinefrom the needled end.

Distal portion 22 includes a retainer with a cartridge 48 held therein.The cartridge retainer is shown formed in majority part as a distalextension 28 of the injection mechanism housing of pen 20, which is madeof an opaque plastic. Windows 29 in extension 28 allow the contents ofthe cartridge to be seen to let a user estimate the medicine remaining.The retainer is formed in additional part as a stepped-down, injectionmolded plastic cap 30 that has a plurality of tabs 32, such as two,three or four tabs on the outer periphery that snap lock duringmanufacture into complementary apertures in extension 28. Other means ofconnecting the cap to the retainer extension may alternatively beemployed, such as adhesives or ultrasonic welding. Suitable connectionmeans, such as external threads, are provided on cap 30 to releasablyconnect a pen-needle assembly, generally designated 34. Not shown crushribs may be molded into the interior of the retainer to hold cartridge48 axially fixed between such crush ribs and an inner surface of the cap30.

Pen-needle assembly 34 is of known design and includes a double-endedneedle cannula or injection needle 36 having a distal tip 37 at one endand a proximal point 38 at the other. Injection needle 36 is mounted ina tubular hub 40 that is structured, such as via internal threading, tocooperate with the shown retainer design so as to be removably mountedto the retainer distal end. A not shown needle cap mounted to the hub,which needle cap is removed when pen 20 is used to inject medicine, mayprotect tip 37. Although the needle assembly is shown as having a singleinjection needle, needle assemblies which may be used with pen 20 may beof various types known in the art, including, but not limited to,assemblies with one or more shortened injection needles, includingmicroneedle arrays.

Cartridge 48 is of conventional design and defines a medicine-filledreservoir 50 that is closed at its proximal end by a piston 52 that isaxially slidably and sealably engaged with the cartridge interior wallto hold the fluid medication within reservoir 50. The distal, outlet endof cartridge reservoir 50 is sealed by a septum 54 held by a cap 56 thatis secured to a stepped-down diameter neck portion 49 of the cartridge.When pen-needle assembly 34 is mounted on cap 30, the proximal point 38of injection needle 36 passes through a central opening in the distalend of cap 30, an opening in cap 56, and penetrates cartridge septum 54to provide a fluid flow outlet by which medicine within cartridgereservoir 50 can be dispensed from needle tip 37 during operations ofinjector pen 20.

The fluid medicine container shown and described above is illustrativeand not intended to be limiting as other constructions may be employedwithin the scope of the invention. For example, rather than the showncontainer in which a distinct cartridge is held by a cap within aretainer portion integrally formed with the rest of the pen housing, inanother fluid container embodiment, the cartridge could be constructedto be sufficiently durable and adapted to secure directly to a penproximal portion 24 without any protective retainer there around, andwith the pen-needle assembly directly mountable to the cartridge. Stillfurther, and similar to other known pens as well as pen 320 of FIGS.22-26, the proximal extension of the housing and the cap 30 shown in pen20 can be eliminated and the cartridge could be slidably inserted andheld in a one-piece retainer that extends the cartridge length, thatremovably mounts a pen needle assembly at its distal end, and that has aproximal end. In the case of a disposable pen, such proximal end can befixedly mounted or secured, via adhesives, ultrasonic welding or inanother suitable manner, to the injecting mechanism housing of anassembled pen portion when its injector pen is assembled by themanufacturer, while in the case of a reusable pen, wherein the retainermay be reusable, such proximal end can be removably mounted or secured,such as via a threaded connection, to a reusable injecting mechanism penportion having a resettable drive member. In this one-piece retainerdesign, the cartridge may be axially constrained directly between theretainer interior surface and a portion of, for example, the housingwithout the use of crush ribs.

With additional reference to FIGS. 4-6, pen proximal portion 24 ofinjector pen 20 includes an external, protective housing 60, an axiallyadvanceable drive member 62, a nut 64, a nut advancing plunger 66, ascrew element 68, and an actuator 70 that is used to set the dose andthen inject the set dose.

Housing 60 is formed from a lightweight material, such as injectionmolded plastic. The housing may be molded as a single, tubular piece forrobustness. The tubular body of housing 60 defines an internal hollow 72in which drive member 62 extends in an axial or longitudinal direction.A window 74 in the housing near its proximal end is shown filled with amagnifying lens 75 that snaps fits to the housing. Lens 75 is optionalin other embodiments and allows dosage indicating markings on a dial tobe readily visible during use. The exterior of housing 60 is formed withone or more elements, such as detents, formed cooperatively with the pencap configuration to allow a removable snap-mounting of pen cap 21 tohousing 60.

Near the distal end of proximal portion 24, housing 60 is formed with aninner annular shoulder 77. A central opening of shoulder 77 is ringed bya proximally extending collar 78 that provides support for drive member62. At least one drive member anti-rotation element extends radiallyinward from collar 78 into hollow 72 and projects distally of the collar78. The shown anti-rotation element is provided in the form of a pair ofdiametrically opposed elements or tabs 80 having squared off inward endsthat each slidably fit within longitudinal keyways 82 in drive member62. In alternate embodiments, features other than tabs and keyways, forinstance a drive member with flats that fits within a complementarilyshaped hole in the collar, may be used to prevent rotation. Tabs 80prevent drive member 62 from rotating within housing 60 during pen use,but permit drive member 62 to be shifted longitudinally, such as in thedistal direction toward the cartridge. Although tabs 80 and shoulder 77are shown integrally formed and therefore rotatably fixed with housing60, a shoulder with tabs may be separately formed and then assembled tothe housing to be rotatably fixed relative thereto. Such assembly forpen 20, which may be accomplished with a snap fit connection of theshoulder to the tubular housing that prevents axial and rotationalrelative motion, may also be accomplished with a shoulder and housingdesign that alone results in a rotational fixing but not a completeaxial fixing of the shoulder and housing, with the axial positioning andsecurement of the shoulder being a result of it being pressed into placeagainst a feature of the housing by the cartridge during pen assembly.In addition, if it is desired to provide the drive member with ananti-backup element, tabs 80 could include teeth that engage an optionalrack within the slots of the drive member, or the tabs could beconstructed to grip into the plastic of the drive member, to prevent thedrive member from being moved within the housing in the proximaldirection during use, but which do not prevent the drive member frombeing advanced in the distal direction toward cartridge 48.

Drive member 62 is in the form of a screw that is axially translatableand rotatably fixed during dosing and injecting. Drive member 62includes a shaft with a helical threading 84 along its length, whichthreading is interrupted by longitudinally extending keyways or grooves82. A thread stop 86 shown at the proximal end of threading 84 isprovided and is used in preventing the pen from being set by a user todeliver a dose of medicine larger than remains in cartridge 48. Threadstop 86 is shown disposed on flanges of the screw defined at theproximal screw end by a diametric relief notch 88, which notch allowsthe thread stop to be cammed in and pass by the nut thread during penassembly, but which thread stop, after passing the nut threads duringassembly, then resiliently returns to a functional position. Other formsof stopping the screw motion may be substituted within the scope of theinvention. For example, in an embodiment where the shaft and foot areseparately formed and then assembled during pen assembly, the notch atthe proximal screw end can be eliminated, and the threading at theproximal screw end could stop near the proximal end where it can not becammed in, and such solid screw with thread stop better ensures the nutwill not be torqued off the screw during dose preparing.

The distal end of drive screw 62 includes an enlarged, disc-shaped foot90 to distribute loading on the cartridge piston 52 that the footcontacts and thereby directly engages during piston advancing. Drivescrew 62 is shown as being a one-piece plastic injection molding. Otherconstructions of the drive member, including as an assembly ofseparately formed component parts as alluded to above, is within thescope of the invention. For example, if, unlike in the assembly sequencedescribed below, the threaded shaft is intended to be moved distallythrough the nut during assembly, such as to allow for a more robustthread stop described above, or to allow the screw to include ananti-backup rack described above, the separate foot can be attached,such as with a snap fit that may permit relative rotation, to thethreaded shaft end previously passed through the nut.

Nut 64 includes a cylindrical, tube-shaped body 92, plunging rib 94,flexible assembly fingers 96 and clicker members 98. The distal regionof body 92 is formed with an internal threading 100 that threadedlyengages in a friction locking fashion the drive screw threading 84.Threadings 100 and 84 are shown as a double start threading but may bedifferently formed while still providing suitable friction lockingcapabilities, such as a single start threading or another multiple startthreading. For a single start threading, threading 100 may extendslightly less than a single turn, and therefore slightly less than 360°,to facilitate molding by allowing use of axial core pins instead of anunscrewing core pin in the molding process. Rib 94 radially protrudesfrom and extends circumferentially around body 92. Referringadditionally to FIG. 7, rib 94 includes a sloped proximal face 95adapted for engagement, such as a direct engagement via abuttingcontact, with plunger 66 during injecting. The hollow interior of nutbody 92 proximal of threading 100 allows free passage of the proximalend of drive screw 62.

The exterior surface of nut body 92 is cooperatively designed withactuator 70 so that the actuator is axially free and rotatably fixedrelative thereto. Thus, during use the actuator is axially moveablerelative to, but rotatably locked with, the threaded nut. Thisconnection is shown obtained using at least one, such as at least two,angularly spaced slots or grooves 102 in the exterior surface of nutbody 92 proximally of rib 94. Grooves 102 extend longitudinally andslidably accommodate keys 122 of nut-engaging sleeve 110.

Assembly fingers 96 serve to prevent nut 64 from coming off plunger 66after being assembled thereto during manufacture. The length of assemblyfingers 96 is defined by U-shaped openings 97 through body 92. Theradially protruding tips of fingers 96 each includes a ramp-shapedproximal face 104, and a distal face 105 aligned perpendicular to theaxis of the nut body.

Clicker members 98 cooperate with complimentary elements provided on thedrive sleeve to provide a clicker function during dose setting. The nutclicker members are shown including at least one, such as two, flexibleconvex webs 106 that bow outward from nut body 92. Each web 106 includesa bi-directional tooth 107 at the center of its length that snaps over,in either direction of rotation, a ring of bi-directional, longitudinalribs 170 formed in drive sleeve 66. Ribs 70 define detents at each ofthe plurality of angular positions corresponding to increments in dosevolume. As few as one clicker element may be provided, but the use oftwo equally angularly spaced teeth as shown, or more teeth, such as fourteeth, equally angularly spaced aids in centering nut 64 within theplunger or drive sleeve designated 66. Nut 64 is shown as being aone-piece plastic injection molding, but other constructions are withinthe scope of the invention.

In the first embodiment, and with primary reference to FIGS. 5 and 6,actuator 70 includes a tubular, cylindrical nut-engaging sleeve 110formed in one piece of an injection molded plastic and which fits withinhousing hollow 72. A flange 112 that rings the proximal end of the body111 of sleeve 110 includes radially extending, square shaped teeth 114.The proximal end of body 111 has a closed face 116, and stem 118 axiallyextends from the center of face 116 in the proximal direction. Adjacentits distal end, the interior surface 120 of body 111 includes a pair ofdiametrically arranged ribs or keys 122 that are slidably received inthe straight keyways 102 formed in nut 64. Although shown as beingfinite in length, keys that extend the entire longitudinal length ofnut-engaging sleeve 110 may facilitate molding.

Actuator 70 also includes a button 126 extending proximally of housing60 in the zero dose pen arrangement. Button 126 is injection molded fromplastic with a disk shaped proximal face 128 and a mounting collar 130centrally located on a distal surface. Button face 128 serves as a pushsurface against which a force can be applied manually (i.e. directly byuser contact) to push the actuator to the left from the perspective of aviewer of FIG. 3. Collar 130 is secured to stem 118, such as with akeyed fit and an ultrasonic weld, so as to axially and rotatably fixtogether button 126 and nut-engaging sleeve 110. Button 126 furtherincludes a depending lip or flange 132 that distally extends from theradial periphery of the button distal face. Lip 132, which serve as agrip portion that is externally accessible to be manually rotated by auser for dose setting purposes, may be knurled or otherwise formed tofacilitate being gripped by a user's fingers.

Coaxially mounted around nut-engaging sleeve 110 is a screw element 68.Screw element 68 serves as the dial in the first embodiment due to doseindicating markings (not shown) provided on its exterior. Screw element68 is formed in one piece of an injection molded plastic and includes acylindrical exterior surface 136 having a threading 138 along a portionof its axial length between the distal end 140 and the proximal end 141.Threading 138 is shown formed by angularly spaced thread sectionsproperly oriented in a helical arrangement, and engages a correspondingthreading 76 formed on the interior surface of housing 60 to threadedlyengage the screw element to the pen housing. Threadings 138 and 76 areshown as a triple start threading but may be differently formed, such asa single start threading or another multiple start threading. For suchtriple start threading, the shown thread sections of 138 correspond tothe three thread starts. Exterior surface 136 is sized to freely insertwithin button 126 such that depending lip 132 is disposed radiallyoutward of and axially extends distally of proximal end 141. Proximalend 141 has an annular face 143 that defines a central opening 145through which fits nut-engaging sleeve stem 118. To serve as adose-indicating dial, screw element 68 includes around its exteriorsurface 136 suitable indicia of therapeutic dose size as visible throughlens 75. When pen 20 is to be used for insulin in which the dosedelivered is desired to be any of a variety selectable by a user, theindicia is provided in the form of a helically arranged pattern ofnumerals, such as from zero to the maximum allowed by the pen, such as60 or 80, in two unit increments, with odd dose sizes being representedby hash marks between the even numbered dose sizes. Different indiciacan be used for different pens, such as if the pen were intended todeliver a fixed dose.

Disposed between screw element 68 and actuator 70 are biasing means usedto urge the components away from each other in an axial direction. Thebiasing means are shown provided in the form of one or more resilientleaf springs or flexures 148 formed, for example, integrally with dial68. In alternate embodiments, different biasing means, such as metalsprings, may be used. Flexures 148 are two in number and extend fromannular face 143 to directly engage or abut the underside of button face128. During injection, when a user manually applies a plunging forceonto proximal face 128, flexures 148 are elastically compressed untilthe small space previously existing between the distal face 131 ofcollar 130 and annular face 143 is closed, and the contacting distalface 131 and annular face 143 then serve together as a thrust bearing.

A hollow interior 149 of screw element 68 is defined by a cylindricalinterior surface 150 provided with a helical threading 152 along itslength. At least one tooth 154, such as two diametrically opposed teethor a ring or teeth, is molded into screw element 68 at the intersectionof annular face 143 and the interior surface 150. Teeth 154, when meshedwith flange teeth 114, serve to rotatably lock together nut-engagingsleeve 110 and screw element 68, and thereby actuator 70 and screwelement 68. Teeth 154 and 114 mesh when the flexures 148 have biased thescrew element 68 and actuator 70 to the arrangement shown in FIGS. 2 and3, and are not meshed or are disengaged when the flexures have beencompressed during injecting to the arrangement shown in FIG. 4, whichnon-meshing permits relative rotation of screw element 68 andnut-engaging sleeve 110. In alternate embodiments, the actuator andscrew element may be differently clutched together. For example, thenut-engaging sleeve may include one or more axially oriented teeth, suchas a ring of four equally angularly spaced teeth, that extend in theproximal direction from face 116 and that are insertable into a circulararray of holes in the screw element annular face 143. In such analternate embodiment, one or more radially extending teeth, such as fourequally angularly spaced teeth, similar to teeth 114 may still beprovided to be engagable with drive sleeve teeth 164 described below tolimit apparatus misuse.

Plunger or drive sleeve 66 is injection molded from plastic and includesa tubular body 160 that fits into the interior hollow 149 at a locationradially outward of nut-engaging sleeve 110. Body 160 slides into andout from housing hollow 72 during pen use. A helical threading 162 isformed on the proximal region of body 160 along its exterior surface.Threading 162 engages the corresponding threading 152 formed on screwelement 68 to threadedly engage the screw element 68 to the drive sleeve66. Threadings 162 and 152 are shown as a double start threading but maybe differently formed, such as a single start threading or anothermultiple start threading. The proximal end of body 160 is notched toform a ring of axially projecting teeth 164 that aid in limiting penmisuse as described below.

Drive sleeve 66 is keyed to the pen housing 60 to be rotatably fixed andaxially moveable relative thereto. In the first embodiment, the keyingis accomplished by at least one, such as a pair of diametrically opposedprongs 166 that axially extend from a flange 168 that radially projectsfrom the distal end of body 160. Prongs 166 are sized and configured tobe slidably received in a pair of diametrically arranged holes 79provided in housing shoulder 77. In alternate embodiments, the keying ofthe housing and the drive sleeve can be differently provided, such asvia radially extending prongs of the drive sleeve that slide within, forexample, axially extending recesses or slots in the housing. Stillfurther, the keying can be accomplished via prongs of the housing thatfit within openings in the drive sleeve, such as one or more prongs thataxially project from shoulder 77 and fit through openings in flange 168of drive sleeve 66.

The hollow interior of the drive sleeve body 160 includes a ring ofaxially extending, bi-directional ribs 170. An annular rib 172 extendstransversely within the hollow at a location proximal of ribs 170. Rib172 includes an angled distal face 174 that serves as an abuttingsurface for the nut 64, and further facilitates assembly by camming downthe ramp-shaped proximal faces 104 of fingers 96 during assembly. Rib172 axially fits in closely spaced relationship with rib faces 105 andrib face 95.

The threaded connections of the screw element and the housing, and thescrew element and the drive sleeve, are non-binding to facilitatebackdriving. Such connections are shown as formed by projecting,square-shaped threads that slide within corresponding designed recessedgrooves or slots. It will be appreciated that the threading can beotherwise configured by the skilled artisan, such as the projectingthreads and grooves being on opposite parts, or with different numbersof starts for the threadings, within the scope of the invention.

From the foregoing description, it will be recognized that as button 126is manually turned during dose setting, the nut-engaging sleeve 110rotatably fixed therewith also turns, and screw element 68 is caused toturn due to the clutched connection provided by the intermeshing teeth114 and 154. Due to its threaded engagement with housing 60, screwelement 68 screws out from the proximal end of the housing, bringingwith it nut-engaging sleeve 110 and button 126 in this screwing motion.As screw element 68 screws out, drive sleeve 66, due to it beingrotatably fixed relative to the housing and in a threaded connectionwith the screw element, is drawn by the screw element proximally andwithout rotation. The rotation of nut-engaging sleeve 110 during thedial screwing out causes a rotation of nut 64 proximally along thethreading of the rotatably fixed drive screw 62.

The threading of screw element 68 to the housing 60, the drive sleeve 66to the screw element 68, and the nut 64 to the drive screw 62, aredesigned together to obtain the mechanical advantage desired by themanufacturer, and further preferably are held within tolerances duringmanufacture such that during the dose setting described above, the drivesleeve 66 moves at the same speed and distance as nut 64 and neitherpromotes nor hinders the motion of nut 64 along the drive screw 62. Inorder to obtain a mechanical advantage of X between the motion of screwelement 68 and drive screw 62 as set by the manufacturer, the threadingof the screw element with the housing has a screw lead equal to X timesthe lead of the drive screw, and the threading of the screw element withthe drive sleeve has a screw lead equal to (X−1) times the lead of thedrive screw, wherein the lead refers to the axial distance traveled in asingle revolution. A suitable mechanical advantage X for an insulin penis believed to include 3 or 4, such as 3.4, and the screw lead of thedrive screw 62 and nut 64 is selected by the manufacturer based upon howmany revolutions or partial revolutions of the dial are desired in orderto set an average dose. A suitable screw lead of the drive screw isabout 0.1 inch, such as 0.108 inch. In addition, to ensure medicationdose not drool from the device during dose setting, it is furtherpreferred that the tolerances are held such that the screw lead of thedrive screw, if not exactly equal to the screw lead of the threading ofthe screw element with the housing minus the screw lead of the threadingof the screw element with the drive sleeve, is slightly less than suchdifference.

Referring now to FIGS. 7-18, one suitable sequence for assemblinginjection pen 20 is described. Such assembly may be performed manually,or alternatively in an automated fashion.

A first step of manufacturer assembly is to axially insert nut 64 intothe drive sleeve 66 as shown in FIG. 7. The insertion proceeds as rib172 engages fingers 96 and cams the fingers inward as the rib slidesover proximal faces 104. When drive sleeve 66 reaches the point at whichrib 172 fits between proximal face 95 and the distal faces 105, theresilient fingers 96 return outward to axially lock nut 64 relative todrive sleeve 66 in a rotatable fashion.

In the next assembly step, nut-engaging sleeve 110 is axially insertedas shown in FIG. 8, such that keys 122 are aligned with and slide intothe longitudinal slots 102 of nut 64.

Next, the subassembly resulting from the FIG. 8 step is inserted intohousing 60 such that prongs 166 of drive sleeve 66 insert throughopenings 79 in housing shoulder 77. A tool may be inserted radiallyinward through molding slots 69 formed in the housing body to hold theprongs inward for proper installation.

As shown in FIG. 10, screw element 68 is first screwed onto drive sleeve66, and then screwed into the housing 60 such that threads 138 and 76engage. As shown in FIG. 11, button 126 is then fixedly attached to thenut-engaging sleeve stem 118. It will be necessary to reach through thesubassembly interior to support the nut-engaging sleeve for the joiningoperation.

Lens 75 is then assembled to housing 60 as shown in FIG. 12. For theattachment features used in the first embodiment, the left-hand foot ofthe lens is first hooked into the housing body, and the right side isthen snapped into place. When lens 75 is assembled to housing 60, thedial 68 is thereafter prevented from being completely screwed out andremoved from the housing, as the underside of lens 75 is designed toform a stop for dial threads 138 at the maximum permitted dose of pen20.

Button 126 is then rotated out, causing screw element 68 andnut-engaging sleeve 110 to rotate out. The screw element 68 is thenclamped along its sides as abstractly represented at 180 in FIG. 13.

Next, while pressing button 126 to the left and rotating it in acounter-clockwise direction, as shown in FIG. 14, the drive screw 62 isaxially inserted into nut 64, and the rotation of nut 64 pulls the screwproximally. Axial pressure on button 126 is then released, the clamping180 is removed, and the button 126, screw element 68 and nut-engagingsleeve 110 are dialed back down as shown in FIG. 15 while the screw 62remains in the same axial and rotational position.

The subassembly of FIG. 15 then receives cartridge 48 as shown in FIG.16, and then, as shown in FIG. 17, cap 30 is secured to the housing body60 to capture cartridge 48 within the pen 20.

After the cartridge is secured, the manufacturer can preadjust pen 20such that a known, for example two dose-unit gap exists between foot 90of drive screw 62 and the cartridge piston 52, regardless of cartridgeand pen component variability. This preadjustment simplifies a user'spriming of the device for initial use. This preadjustment involvesdialing out and clamping the screw element 68 as described with respectto FIG. 13 above, pressing and spinning button 126 in the clockwisedirection and without axial motion of the screw element until athreshold torque is met that signals contact by screw foot 90 withcartridge piston 52, and then spinning the button back counterclockwiseby a particular amount, such as, in the case of a two dose-unitrotation, approximately 36° in one embodiment. Next, the screw element68 is released and the button 126 is allowed to automatically pop outunder the influence of flexures 148. Button 126 and dial 68 are thenscrewed back down to a dose setting of zero, and the pen 20 is arrangedas shown in FIGS. 1 and 2.

Cap 21 then can be axially aligned as shown in FIG. 18 and inserted ontothe readied pen, and a label can be wrapped to the housing proximalportion.

The structure of injector pen 20 will be further understood in view ofthe following explanation of its operation. Initially, a user requiringa dose of medication will locate pen 20, which pen is typically in theready or zero dose arrangement shown in FIG. 1, which is the arrangementin which the pen is provided to a user for its first use, or in whichthe pen remained after its previous use.

Pen 20 with a needle attached should first be primed, which priming stepwill be described but briefly as the internal workings of the pen duringthis operation will be appreciated from the further explanation belowwith respect to its injecting operation. In particular, typically whileclutching the housing 60 in one hand, a user manually grips buttonflange 132 and then begins to turn button 126 relative to the housing60. At the zero dose arrangement, and as long as button 126 is not alsobeing plunged which is improper, button 126 can only be rotated in adose increasing direction due to the dial not being further movabledistally. At the zero dose arrangement, if a user attempts to pushbutton 126 distally while turning it, which motion could affect theposition of drive screw 62, such turning of the button is prevented bythe meshing of nut-engaging sleeve teeth 114 with drive sleeve teeth164. A user stops the rotating after a short amount of actuator travelthat is associated with a small delivery volume, such as one or twounits, which is indicated by the markings visible through lens 75. Then,and after removing cap 21 and any other needle cap present, and whilepointing the needle tip 37 upward, the user applies a plunging force onbutton 126 to drive it distally until the screw element 68 returns tothe zero dose position, at which the screw element threading 138 hasreached the distal end of the housing threading 76, during whichplunging action the piston 52 is shifted forward within cartridge 48. Ifa user sees that the piston movement has caused liquid to reach theneedle distal tip 37, the priming process is complete. If no liquid isvisible at needle tip 37, the priming steps are repeated as needed.

After priming, pen 20 is ready to be used for an actual injection.First, a user prepares the pen by setting the desired dose, as visiblein lens 75, by turning of button 126. If the user dials up too large ofa dose, and without expelling any medicine, the user can rotate down thedial by turning the button in the opposite direction, all the way backto zero if desired. After dose setting, the pen is generally arranged asshown in FIG. 3. To inject the dose, after pen 20 is manipulated so theinjection needle distal tip 37 properly penetrates, for example, auser's skin, an axial, distal plunging force is applied to button face128 to force actuator 70 distally toward the housing, such as with athumb or index finger of the hand which grasps the housing. Initiallyduring injecting, actuator 70 is shifted axially and without rotationrelative to dial 68, which shifting motion compresses the biasingsprings 148 to close the gap between button surface 131 and drive sleevesurface 143. The biasing springs are designed to compress prior to thedial 68 moving relative to the housing 60. When actuator 70 shiftsrelative to the dial 68 to the axial arrangement of the nut-engagingsleeve and dial shown in FIG. 4, the clutch teeth 114 and 154 disengageto allow a backdriving rotation of the dial relative to the actuator.During the axial movement of actuator 70 relative to dial 68, nut 64does not move axially or rotationally. When the dial rotatably uncouplesfrom the actuator 70, as the actuator is continued to be axially plungedwithout rotation by the user by the plunging of button 126, the dial 68screws into the housing 60 as it spins relative to button 126 and thedose markings on the dial that indicate the amount still remaining to beinjected is visible through lens 75. As it screws down, dial 68 causesdrive sleeve 66 to in essence screw up the dial 68 threading as thedrive sleeve advances distally a lesser distance than the dial. Theadvancement of drive sleeve 66, due to the abutting or direct engagementof rib 172 with the nut rib face 95, advances nut 64 without rotation,which due to its threaded connection with the screw advances the screwaxially without rotation, which screw advancement shifts cartridgepiston 52 to expel medication from the cartridge reservoir. Theinjection is completed when the screw element threading 138 has reachedthe distal end of the housing threading 76, at which time pen 20 is onceagain arranged in the ready state or zero dose position shown in FIGS. 1and 2.

Pen 20 can continue to be used to deliver any desired dose until themedicine remaining in the cartridge is insufficient for a proper dosing.This insufficiency is indicated to a user by her inability to fully setthe desired dose due to nut threading 100 abutting thread stop 86 ofdrive member 62, at which time the nut and actuator can not be rotatedproximally any farther. When insufficient medicine remains, pen 20 is tobe disposed of and replaced with a similar but entirely new pen.

Referring now to FIG. 19, there is shown portions of another injectorpen of the present invention, which pen is generally designated 200.Other than differences that are described below, pen 200 is identical topen 20, and corresponding parts are identified with a prime reference.Pen 200 is designed differently from pen 20 to provide a nut and plungerengaging surface with a larger diameter, which can be used to betterresist the nut from rotationally slipping relative to the plunger duringinjecting.

Nut 64′ includes two sets of longitudinally extending ribs 202 thatradially project from the nut body. The two sets of ribs each span 90°of the body circumference and are centered 180° apart, resulting in thenut body including around its entire circumference a series of four 90°segments alternately provided with and without ribs. Ribs 202 areaxially disposed between a ramped shaped annular rib 204 and angledannular flange 206. Drive sleeve 66′ is integrally formed with fouraxially-extending, resilient fingers 208 each with its own toothed bead210. Fingers 208 with heads 210 are centered at 90° intervals around thedrive sleeve circumference. All of heads 210 of fingers 208 snap overrib 204 during assembly, and facing pairs of beads 210, at differenttimes of nut rotation, snap over ribs 202 to provide a dose-identifyingclicking function during relative rotation of nut 64′ and drive sleeve66′. This finger and rib design facilitates molding while providing asuitable balancing of forces on the nut. If in an alternate embodimentthe ribs were to extend continuously around the nut circumference, onlytwo fingers centered 180° apart may be employed while still providingsuitable force balancing. A flange 214 extending between the drivesleeve body and the locking prongs 166′ has an angled or frustroconicalinterior surface 216. Flange surface 216 is adapted to frictionallyengage the circumferential lock surface 220 of nut 64′ during injecting.Interior surface 216 and lock surface 220 may have the showncross-sectional shape around their entire peripheries. During injecting,as drive sleeve 66′ is advanced distally to thereby simultaneouslyadvance nut 64′, the nut and drive sleeve are suitably rotatably fixedtogether by the frictional locking of the contacting conical surfaces.

Referring now to FIGS. 20 and 21, there is shown portions of anotherinjector pen of the present invention, which pen is generally designated250. Pen 250 is conceptually similar in many respects to pen 20 of FIGS.1-18, and corresponding parts are identified with a double primereference, but pen 250 is adapted for use as a reusable device in whichthe held medicine cartridge can be removed when spent and replaced witha new cartridge.

In pen 250, the housing generally referenced at 60″ is internallythreaded at 252 and is adapted to threadedly receive the reusablecartridge holder or retainer 254 in which medication cartridge 48 isremovably mounted. A tubular cartridge seat 258 rotationally keyed tohousing 60″ in a not shown fashion is biased distally by a spring 260that abuts an annular face of seat shoulder 262 and the distal face ofhousing shoulder 77″. The interior surface of seat 258 includes a ringof inwardly facing ribs or keys 270.

A tubular lock sleeve 272 includes prongs 274 to snap fit to a housingcollar 276 to allow sleeve 272 to be rotatably free and axially fixedrelative to housing 60″. Lock sleeve 272 includes a pair of not shown,diametrically opposed, inwardly extending tabs that insert within thelongitudinal grooves of drive screw 62″ to allow drive screw 62″ to berotatably fixed and axially free relative to lock sleeve 272. Locksleeve 272 includes at least one, such as a plurality of, radiallyoutwardly facing teeth 280 that are complimentarily designed tocartridge seat ribs 270 to rotatably lock together lock sleeve 272 andseat 258 when engaged.

When a cartridge is installed as shown in FIG. 20, cartridge seat 258 isforced to its retracted or proximal position at which ribs 270 mesh withteeth 280. The resulting rotational locking of lock sleeve 272 to therotationally locked seat 258 results in screw 62″ being rotatably fixedwithin the housing, and reusable pen 250 can be operated similar to pen20. When the cartridge is spent and retainer 254 is removed as shown inFIG. 21 to install a replacement cartridge, cartridge seat 258 travelsto the extended position shown in FIG. 21, at which position it isaxially retained within the housing in any suitable fashion, and atwhich lock sleeve teeth 280 are released and clear of ribs 270. As such,lock sleeve 272 is free to rotate with the drive screw 62″ and relativeto the housing 60″ as the drive screw is pressed back, and therebyscrewed into the axially stationary nut 64″, to its starting positionfor use with the next cartridge. Drive screw 62″ is shown in FIG. 21after having been so pushed back. Although shown as having a one-piececonstruction, the drive screw 62″ may be provided with a rotatablyfloating foot at its distal end to promote its back drive-ability.

In a not shown embodiment, the present invention may include an end ofinjection indicator that provides notice to the user that the pen is inthe ready or zero dose position. One such indicator may include aresilient arm with a toothed end which projects from the proximal faceof a shoulder or bulkhead similar to shoulder 77 of pen 20. The shouldermay be formed separate from but suitably attachable to the housing, andthe arm with tooth may be integrally formed with such shoulder. Theannular, distal face of the screw element or dial includes a detentwhich the clicker arm tooth snaps over when the screw element has beenfully screwed distally or backdriven into the housing during injecting,which snapping motion provides a tactile and audible notice that theinjection process has been completed, but which detent and toothengagement does not prevent the screw element from being rotated outduring dose preparing. To properly positively stop the distal travel ofthe screw element, and as is conveniently possible with a separatelyformed shoulder, a hard distal stop to prevent further dial screwing maybe formed by the shoulder to be abutted by the screw element externalthreading at the zero dose position. For a pen with such a shoulder, andalthough an assembly sequence different than shown with respect to pen20 would be required, the housing body could be molded such that theproximal end of screw element travel can be halted by a thread stopwithin the housing body which is abutted by the screw element externalthreading, and no lens, if not otherwise necessary for magnification orother purposes, would be required as the screw element disassemblyfunction served by the lens of pen 20 is not needed.

In another not shown embodiment, the present invention may be modifiedto move threading 162 distally on the plunger body from the proximalregion shown, which movement allows the axial length of threading 152 ofscrew element 68 to not extend as far proximally. Still further, such adesign allows the plunger 66 to be shorter, as the plunger bodyproximally of the moved threads may be eliminated. To limit pen misuse,teeth 164 would be included on the new proximal end of the plunger body,and one or more radially extending teeth, such as four equally angularlyspaced teeth, similar to teeth 114 would be moved distally on thenut-engaging sleeve to be properly engagable with the drive sleeve teeth164.

Referring now to FIGS. 22-26, there is shown still another embodiment ofa medication dispensing apparatus of the present invention. Theapparatus, generally designated 320, is functionally similar to pen 20,and embodies a currently preferred overall configuration. Medicationinjector pen 320 is a prefilled, variable dose pen, suitable fordelivery of any of a variety of therapeutics, such as insulin. Injectorpen 320 generally includes a distal portion 322, which is receivedwithin pen cap 321 in FIGS. 22 and 23, and a proximal portion 324.

Distal portion 322 includes a retainer with a cartridge 348 heldtherein. The cartridge retainer is provided in the form of a tubularbarrel 328 made of transparent plastic. Internal, longitudinallyextending ribs 329 support the cartridge. An orienting skirt 326 of thebarrel 328 is shaped to engage and automatically properly rotationallyorient cap 321 when the cap is slid onto the cartridge retainer. Twosnaps 331 on barrel 328 fit over a circumferential detent 333 formed inthe interior of cap 321 to allow a releasable attachment of cap 321. Ascap 321 is somewhat squarish in cross-section, the four slots 335 inbarrel 328 provide clearance for the cap detent 333 when the cap issnapped on. The proximal end of barrel 328 is fixedly secured during penassembly, such as with adhesives, to a mounting flange 373 of bulkheadportion 330 of the pen housing. Connection means, such as externalthreads 332, are provided on a stepped-down distal end of barrel 328 toreleasably connect a known pen-needle assembly 334 that includesinjection needle 336, hub 340 and needle cap 338. Cartridge 348 is ofconventional design and includes reservoir 350, piston 352, septum 354and cap 356.

Pen proximal portion 324 includes an external, protective housing 360,an axially advanceable drive member 362, a nut 364, a nut advancingplunger 366, a screw element 368, and an actuator 370 that is used toset the dose and then inject the set dose.

Housing 360 is formed from injection molded plastic bulkhead portion 330and tubular body portion 371. A mounting flange 376 of bulkhead portion330 inserts within and is fixedly secured, such as with adhesives, tobody portion 371 during manufacturing assembly. Two diametricallyopposed cutaways 385 are included in flange 376 to provide clearance forthe distal end of screw element 368. Only one of cutaways 385 isactually used but two are provided to lessen the need for rotationalorientation during assembly. Bulkhead portion 330 and body portion 371are also keyed together via tab 361 and a slot 374 in a circumferentialridge around the bulkhead, which keying further ensures that the fixedconnection of the housing pieces prevents relative rotation. Thebulkhead ridge is shown with two such slots 374 spaced 180° apart tofacilitate assembly.

Body portion 371 defines an internal hollow 372 in which drive member362 extends in an axial direction. Housing window 375 allows dosageindicating markings on a dial portion within the housing to be readilyvisible during use.

Housing bulkhead portion 330 is formed with an inner annular shoulder377 having a central opening ringed by boss 378. A pair of diametricallyopposed tabs 380 extend inward from shoulder 377 into hollow 372. Tabs380 slidably fit within longitudinal keyways 382 in drive member 362 toprevent drive member 362 from rotating within housing 360 during penuse, but permit drive member 362 to be shifted longitudinally. Anopening-ringing boss with four equally angularly spaced, radiallyextending legs 381 distally project from shoulder 377, and the legsserve as abutments for the installed cartridge. Two diametricallyopposed lugs 388 are formed on the interior surface of mounting flange376 in axially spaced relationship with shoulder 377.

Drive member 362 is in the form of a screw that is axially translatableand rotatably fixed during dosing and injecting. Drive member 362includes a shaft with a helical threading 384 along its length, whichthreading is interrupted by the longitudinally extending keyways orgrooves 382. A thread stop 386 at the proximal end of threading 384prevents the pen from being set by a user to deliver a dose of medicinelarger than remains in cartridge 348. Drive member 362 engages thecartridge piston via an enlarged, disc-shaped foot 390 that snap fits toa mushroom-shaped head 389 formed at the end of drive member 362 so foot390 is axially fixed to the drive member. Foot 390 is rotatable for thehead shown, but need not be so to function appropriately for thisembodiment.

Nut 364 is made from injection molded plastic and includes acylindrical, tube-shaped body 392, plunging rib 394 and a pair of torquefingers 396. The distal region of body 392 is formed with an internalthreading 400 that threadedly engages the drive screw threading 384 in afriction locking, or non-back-drivable, fashion. Threadings 400 and 384are shown as a double start threading. Rib 394 radially protrudes fromand extends circumferentially around body 392, the proximal face ofwhich rib is directly engaged via abutting contact with plunger 366during injecting. The distal face of rib 394 abuts bulkhead boss 378when the nut is fully advanced to halt drive member movement, andthereby screw element movement, during an injection. Strengthening ribs395 project from the distal face of rib 378, but have a larger insidediameter than the outside diameter of boss 378.

A circumferential recess 398 in the radial periphery of body 392includes a series of axially extending ribs 399 that cooperate withcomplimentary elements provided on drive sleeve 366 to provide a clickerfunction during dose setting in either dose increasing or dosedecreasing directions. In the shown embodiment, ribs 399 are provided intwo 90° angular segments spaced by 90° ribless segments so as tocooperate with the four equally angularly spaced finger members providedon the drive sleeve. Torque fingers 396 are cooperatively designed withactuator 370 so that the actuator is axially free and rotatably fixedrelative thereto.

In the shown embodiment, actuator 370 includes a nut-engaging sleeve 410formed in one piece of an injection molded plastic and which fits withinhousing hollow 372. A flange 412 that rings a central region of the body411 of sleeve 410 includes splines or teeth 414 that extend from thedistal face of flange 412, and teeth 415 that extend from the proximalface of flange 412. A stepped-down portion of body 411 forms an axiallyextending stem 418. The distal end of body 411 includes a pair offingers 420 that interfit with torque fingers 396 as to allow axialmotion but not rotational motion of the nut 364 relative to the sleeve410, thereby rotationally locking the pieces together within the sameannular space. Fingers 396 and 420 extend sufficiently axially to ensurethey do not disengage during the preparing of the maximum pen dose forinjection. While fingers 396 and 420 are shown as pairs arrangeddiametrically, with each finger spanning 90°, different numbers andshapes of interfitting elements may be used within the scope of theinvention.

Actuator 370 also includes an injection molded plastic button 426 withproximal face 428, and a distally facing and centrally located bearingcollar 430 and alignment post 431. Stem 418 receives post 431 and isultrasonically welded within collar 430 during manufacturing assembly,so as to axially and rotatably fix together button 426 and nut-engagingsleeve 410. Button lip 432 distally extends from the radial periphery ofthe button distal face to serve as a grip portion.

Coaxially mounted around nut-engaging sleeve 410 is screw element 368.Screw element 368 is formed in two injection molded plastic pieces by amain portion 402 and a flange 404. The cylindrical exterior surface 436of screw element main portion 402 has a threading 438 formed as ahelical groove that engages a corresponding threading 379 formed on theinterior surface of housing body portion 371 to threadedly engage thescrew element to the pen housing. Threadings 438 and 379 are shown as asingle start threading but may be differently formed. Threading 379abuts the end 439 of threading 438 at the maximum pen dose, assuming thecartridge is sufficiently full for such a maximum dose. A stop surface437 of main portion 402 is positioned in slightly spaced apartrelationship with a projecting stop 463 at the zero dose position, andstop surface 437 is to be abutted by stop 463 if a user attempts tomanually screw the screw element below a zero dose position. Exteriorsurface 436 is sized to freely insert within button 426 such thatdepending lip 432 is disposed radially outward of and axially extendsdistally of the proximal end of screw element main portion 402.

A hollow interior 449 of screw element main portion 402 is defined by acylindrical interior surface 450 provided with a helical threading 452.Threading 452 is shown as an inwardly projecting thread that spans about350° of the interior. The proximal end region of main portion 402includes three notches 405 and three windows 406 that are alternatelyspaced around the circumference. Screw element main portion 402 includesaround its exterior surface 436 suitable indicia of therapeutic dosesize as visible through housing opening 375.

The tubular flange 404 fits within the open proximal end of main portion402. Ears 407 fit within notches 405 and assembly fingers 408 snap lockinto windows 406 to axially and rotatably lock the screw elementcomponents 402 and 404 together during manufacturing assembly. A ring ofaxially extending teeth 409 formed in the interior surface of flange 404cooperate with actuator teeth 415.

Disposed between the screw element 368 and actuator 370 is a taperedmetal spring 448 that urges those components away from each other in anaxial direction. A larger diameter end of spring 448 directly engagesthe underside of button face 428, and the smaller diameter, opposite endof spring 448 directly engages an apertured end face 403 of flange 404.During injection, when a user manually applies a plunging force ontoproximal face 428, spring 448 is elastically compressed until bearingcollar 430 contacts flange face 403 to serve as a thrust bearing. Flangeteeth 409 and teeth 415 mesh when spring 448 has biased the screwelement 368 and actuator 370 to the arrangement shown in FIG. 23, andare not meshed when the spring has been sufficiently compressed duringinjecting. While a tapered, helically coiled metal wire spring is shown,other forms of commonly known biasing elements may be substituted.

Plunger or drive sleeve 366 is injection molded from plastic andincludes a tubular body 460 that fits into screw element hollow 449, anda helical threading 462 that engages screw element threading 452.Threadings 462 and 452 are shown as a single start threading, but may bedifferently formed. The proximal most portion of the end of body 460,which end is partially helically shaped corresponding to the threading,is notched to form a partial ring of axially projecting teeth 464 that,when meshed with actuator teeth 414, serve to rotatably lock togetheractuator 370 and plunger 366.

Drive sleeve 366 is keyed to pen housing 360 via a pair of ridge-definedslots 466 on the periphery of sleeve 366 which axially, slidably receivethe lugs 388 radially inwardly projecting from housing bulkhead 330.Openings molded into drive sleeve 366 define four resilient fingers 440having radially inwardly projecting teeth 441 that are axially orientedand shaped to project into recess 398 and click over, in eitherrotational direction, ribs 399 during dose setting. Fingers 440 withteeth 441 cooperate with recess 398 to hinder nut 364 from coming offplunger 366 after being assembled thereto during manufacture.

To facilitate back-driving in the embodiment of FIGS. 22-26, thethreaded connections of the screw element and the housing, and the screwelement and the drive sleeve, are non-binding and provided byprojecting, 60° face angle threads that slide within correspondinglydesigned recessed grooves. With these threadings, it is preferred thatthe mechanical advantage is 3.4 or greater, and the screw lead of thedrive member is 0.108 inch.

While this invention has been shown and described as having variousdesigns, the present invention may be modified within the spirit andscope of this disclosure. For example, to deliver a fixed dose, the penwould preferably be modified such that the maximum that the dial couldbe screwed out to prepare the pen for injection would correspond to thefixed dose. Such a fixed dose pen could eliminate numerical dosageindicating marking, and instead provide user cues in the form of, forexample, instructions and a graphical dosing indicator. This applicationis therefore intended to cover any variations, uses or adaptations ofthe invention using its general principles. Further, this application isintended to cover such departures from the present disclosure as comewithin known or customary practice in the art to which this inventionpertains.

1. A medication dispensing apparatus comprising: a housing; a drive member rotatably fixed during dose preparing and injecting and axially movable in a distal direction relative to said housing, said drive member including a threaded shaft; a fluid container defining a medicine-filled reservoir with a movable piston at one end and an outlet at the other end, said piston engagable by said drive member to be advanced toward said outlet when said drive member is moved distally; a nut screwable along said drive member threaded shaft; a screw element threadedly engaged with said housing to be screwable relative to said housing; a nut rotating element connected with said nut to be axially movable and rotatably fixed relative thereto, said nut rotating element rotatably fixed with said screw element when said nut rotating element and said screw element are in a first axial arrangement, said nut rotating element rotatable relative to said screw element when said nut rotating element and said screw element are in a second axial arrangement; a nut advancing plunger threadedly engaged with said screw element, said plunger axially movable and rotatably fixed relative to said housing; wherein the threading of said screw element to said housing is of a first lead, the threading of said plunger to said screw element is of a second lead, and the threading of said drive member threaded shaft is of a third lead, and said first lead, said second lead and said third lead are each a different value; wherein during dose preparing, said nut rotating element and said screw element are in said first axial arrangement, whereby a screwing motion of said nut rotating element and screw element relative to said housing screws said nut rotating element and said screw element a first axial distance from a home position, which screwing motion of said nut rotating element screws said nut along said drive member threaded shaft a second axial distance different than said first axial distance; and wherein during dose dispensing, said nut rotating element and said screw element are in said second axial arrangement, whereby a screwing motion of said screw element relative to said housing back toward said home position advances said plunger in said distal direction to axially advance said nut and thereby said drive member and said fluid container piston to dispense medicine from said outlet.
 2. The medication dispensing apparatus of claim 1 wherein said nut rotating element comprises a sleeve portion within said screw element and a manually engageable button portion external to said screw element, said sleeve portion and button portion axially and rotatably shiftable as a unit.
 3. The medication dispensing apparatus of claim 2 wherein said button portion is manually plunged during dose dispensing.
 4. The medication dispensing apparatus of claim 3 wherein said button portion is manually rotated during dose preparing.
 5. The medication dispensing apparatus of claim 2 wherein said button portion comprises a depending lip positioned radially outward of and axially extending distally of a proximal end of said screw element.
 6. The medication dispensing apparatus of claim 2 further comprising means for biasing said nut rotating element and said screw element from said second axial arrangement toward said first axial arrangement.
 7. The medication dispensing apparatus of claim 6 wherein said screw element and said nut rotating element comprise interfitting teeth that disengage when said biasing means are overcome to shift said nut rotating element and screw element from said first axial arrangement to said second axial arrangement.
 8. The medication dispensing apparatus of claim 6 wherein said screw element comprises said biasing means that directly engage an underside of said button portion to force said button proximally relative to said screw element.
 9. The medication dispensing apparatus of claim 1 wherein said screw element comprises a tubular member having a radially inner surface and a radially outer surface, wherein said outer surface is threaded to said housing, and wherein said inner surface is threaded to said plunger.
 10. The medication dispensing apparatus of claim 1 wherein said nut comprises an extension having an axially extending keyway in an external surface, and wherein said nut rotating element comprises a key that slides within said keyway.
 11. The medication dispensing apparatus of claim 1 wherein said nut and said nut rotating element comprise interfitting fingers that share an annular space.
 12. The medication dispensing apparatus of claim 1 wherein said nut and said nut advancing plunger comprise cooperating clicker elements for creating audible indications during dose preparing.
 13. The medication dispensing apparatus of claim 1 wherein said first lead equals a factor M times the third lead, and wherein said second lead equals a factor (M−1) times the third lead.
 14. The medication dispensing apparatus of claim 1 wherein said nut advancing plunger is axially movable and rotatably fixed relative to said housing by at least one prong of said plunger that slidably fits within at least one opening formed in said housing.
 15. The medication dispensing apparatus of claim 1 wherein said housing comprises a tubular body portion and a bulkhead portion that are adhesively fixedly secured together, said bulkhead portion including tabs that slidably fit within keyways in said drive member to prevent rotation of said drive member within said housing, wherein said nut advancing plunger is axially movable and rotatably fixed relative to said housing bulkhead portion by at least one lug of said housing bulkhead portion that slidably fits within at least one slot formed in said plunger.
 16. The medication dispensing apparatus of claim 1 wherein said nut advancing plunger includes at least one flange that directly frictionally engages at least one flange of said nut during dose dispensing to resist nut rotation.
 17. The medication dispensing apparatus of claim 9 wherein said screw element serves as a dial and comprises dose indication markings on said radially outer surface.
 18. The medication dispensing apparatus of claim 1 wherein insulin is the medicine within the reservoir.
 19. The medication dispensing apparatus of claim 1 further comprising a plurality of teeth on said nut advancing plunger that are engageable with at least one tooth on a portion of said nut rotating element to limit apparatus misuse.
 20. The medication dispensing apparatus of claim 1 further comprising clicking means for identifying a dose setting, said clicking means including two sets of longitudinally extending ribs radially projecting from said nut, each set spanning 90° of the nut circumference and centered 180° apart from the other set, said clicking means further including four axially-extending, resilient toothed fingers of said plunger, said toothed fingers centered at 90° intervals around the circumference of said plunger.
 21. The medication dispensing apparatus of claim 1 further comprising means for indicating an end of injection, said indicating means including a resilient arm with a toothed end which projects from and is integrally formed with a proximal face of a bulkhead separately formed and rotatably fixed to said housing, said indicating means further including a detent on an annular, distal face of said screw element which said toothed end of said arm snaps over when said screw element is frilly screwed distally into said housing during injecting, and wherein a portion of said bulkhead is abutted by and thereby forms a hard stop for said screw element when said screw element is fully screwed distally into said housing.
 22. A medication dispensing apparatus comprising: a housing; a drive member rotatably fixed during dose preparing and injecting and axially movable in a distal direction relative to said housing, said drive member including a threaded shaft; a fluid container defining a medicine-filled reservoir with a movable piston at one end and an outlet at the other end, said piston engagable by said drive member to be advanced toward said outlet when said drive member is moved distally; a nut screwable along said drive member threaded shaft; a screw element threadedly engaged with said housing to be screwable relative to said housing; a nut rotating element connected with said nut to be axially movable and rotatably fixed relative thereto, said nut rotating element rotatably fixed with said screw element when said nut rotating element and said screw element are in a first axial arrangement, said nut rotating element rotatable relative to said screw element when said nut rotating element and said screw element are in a second axial arrangement; a nut advancing plunger threadedly engaged with said screw element, said plunger axially movable and rotatably fixed relative to said housing; wherein the threading of said screw element to said housing is of a first lead, the threading of said plunger to said screw element is of a second lead, and the threading of said drive member threaded shaft is of a third lead, wherein said first lead equals a factor M times the third lead, and wherein said second lead equals a factor (M−1) times the third lead; wherein during dose preparing, said nut rotating element and said screw element are in said first axial arrangement, whereby a screwing motion of said nut rotating element and screw element relative to said housing screws said nut rotating element and said screw element a first axial distance from a home position, which screwing motion of said nut rotating element screws said nut along said drive member threaded shaft a second axial distance different than said first axial distance; and wherein during dose dispensing, said nut rotating element and said screw element are in said second axial arrangement, whereby a screwing motion of said screw element relative to said housing back toward said home position advances said plunger in said distal direction to axially advance said nut and thereby said drive member and said fluid container piston to dispense medicine from said outlet. 